Process of desensitizing photo-sensitive silver compounds



UNITED STATES PATENT OFFICE.

NATHAN SULZIBERGER, or NEW YORK, N. Y.

Specification of Letters Patent.

No Drawing. Application filed December 10, 1914. Serial No. 876,495. Renewed September 7, 1920. Serial No. 408,776.

To all whom it may concern Be it known that I, NATHAN SULZBERGER, a citizen of the United States, resident of New York city,'in the county and State of New York, have invented new and useful Improvements in Processes of Desensitizing Photo-Sensitive Silver Compounds and Products Produced Thereby, of which the following is a specification.

This invention relates to improvements in the desensitizing of photo-sensitive silver compounds of films, plates, prints, and like photographic reproductions, and to the improved products produced thereby or resulting therefrom.

The invention is based upon the discovery that photo-sensitive silver compounds commonly used in" photography, particularly silver chlorids, can be made fast toward the action of light or more or less completely desensitized toward light, by treating them with a suitable desensitizing solution containing therein a compound of a metal of the platinum group having a desensitizing action upon such silver compounds. As the result of the treatment to which the negatives, prints, films and the like, containing the photo-sensitive silver compounds, are subjected, they are prevented from fading as they would otherwise do under the action of light, and they are given an improved and characteristic composition well adapting them for purposes and uses, when photographic reproduction is desired.

As an example illustrative of the process of the present invention, and the production of the improved product of the invention, the following more detailed description may be given:

A print on photographic paper, which contains such light-sensitive silver salts as silver chlorid, and which is used for copying negatives in daylight, is treated with a very weak solution of a palladium compound having a desensitizing action upon the sensitive silver compound or compounds present.

A solution of readily soluble palladiumammonium-proto-chlorid dissolved in water is well adapted for the desensitizing solution. The bringing of the print into contact wth the palladium solution results in the desensitizing of the silver compounds so that thev are fixed against the action of light. If a part only of theprint is subby the lightening or 'jected to the palladium solution, and then the Whole print, including both the treated and untreated parts, are exposed. to the action of light, all those parts of the print which have not been treated with the palladium solution will soon become dark and be destroyed for useful photographic purposes.

The treatment of the print or like photographic reproduction with the desensitizing solution makes it unnecessary, accordingly, to subject the same to an after-treatment with a solvent for removing the silver ohlorid, something which has heretofore.

been considered unavoidable because of the highly sensitive character toward light of the silver chlorid.

paper, very markedly brightens up the print and especially those parts of the print which have by over-exposure to light during the-printing process, become objectionably dark. portions of prints can frequently be saved brightening thereof resulting from the treatment according to the present invention; so that from one viewpoint, the process of the present invention may be considered as involving both a desensitizing of the silver compounds and a brightening of dark over-exposed prints containing silver compounds.

Another advantage of the present invention is that it avoids the necessity of using and therefore of removing all traces of sodium thiosulfate, which has almost exclusively been used heretofore as a solvent for the still-sensitive silver salts of the print; so that the present process enables the saving of considerable time and of large amounts of water commonly heretofore required.

From the above description it will be seen that the desensitizing treatment is one applied directly to the prints or other photographic reproductions containing the lightsensitive silver compounds, and that this cases, as when using daylight copying Such over-exposed prints or those skilled in the art,.are to be considered A it as coming within the scope of the invention and of the appended claims. Accordingly, mixtures of the metal compounds belonging to the platinum grou) and having the desired desensitizing properties, may be employed.

The term platinum group includes: platinum, iridium, osmium, palladium, ru-

ihenium and rhodium.

In referring to divalent metal of the platinum group, and to compounds of such metal, the term divalent is intended to include not only desensitizing divalent soluble compounds of a metal or of metalsbelonging to the platinum group, but also mixtures containing the same which are efficient in des'ensitizing towardthe action of light a photographic reproduction such as a photo printon paper (a positive) or the develo ed print on a plate or film (a negative). include also such. mixtures of compounds of metals of the platinum group which will reduce a higher valency of the metal or metals of this group to the divalent form, and which are similarly efficient in the desired desensitizing action.

The claims are intended also to include mixtures of the soluble desensitizing compounds of a metal or metals belonging to the platinum group with other substances which do not destroy or interfere with the desired desensitizing action of the compound or compounds of the platinum metal or metals employed.

I claim:

1. The process of desensitizing toward the action of light, photo prints, films and like photographic reproductions containing light sensitive silver compounds, which comprises treating the same with a solution of palladium-ammonium-proto-chlorid.

2. The method of desensitizing photo prints, films, and like photographic reproauctions containing light-sensitive silver chlorid, which comprises subjecting the same to treatment with a-solution of palladium, ammonium-proto-chlorid. I v

3. A desensitized photographic reproduction containingsilver compounds, said reproduction having the silver compounds thereof desensitized by treatment with a desensitizing compound of a metal of the platinum group, the said photographic reproduction containing in addition to silver constituents which have been reduced by the action of light, also silver constituents which have not been reduced by the action of light but'which have been desensitized.

desensitized photographic reproduction containing silver compounds, said reproduction having the silver compounds thereof desensitized by treatment with palladium-ammonium-proto-chlorid, said photographic reproduction containing in addition to silver constituents which have been .reduced by the action of light, also silver constituents which have not been reduced by the action of light but which have been desensitized.

5. A desensitized photographic reproduction containing silver chlorid, which has been desensitized by treatment with a desensitizing compound of a metal of the platinum group, and still containing silver compounds soluble in sodium thio-sulfate.

6. A desensitized photographic reproduction on a sensitized medium containing silver compounds, said reproduction containing, in addition to silver constituents which have been reduced by the action of light, also silver constituents originally sensitive and which have not been so reduced but have been desensitized without dissolution.

- NATHAN SULZBERGER.

Witnesses:

CHARLES FISCHER, ALBERT O. STOCKER. 

